Acquired Immunodeficiency Syndrome (AIDS) is characterized by a breakdown in the immune system that manifests itself in the form of serious, life-threatening oppor-tunistic infections (OI). Therapy of AIDS-related OI is inadequate due to a number of factors, among the most important of which is the absence of any truly effective antibiotics. As part of other projects to discover novel prototype antibiotics for AIDS-related OI, two natural products (eupolauridine and liriodenine) were discovered to exhibit promising in vitro activity against the major AIDS-related fungal and bacterial OI pathogens, as well as in vivo efficacy in animal models of disseminated mycoses. The proposed project is aimed at determining the structure-activity-relationships (SAR) of one of these prototype natural products, eupolauridine, which has demonstrated activity against Cryptococcus neoformans, Candida albicans, Aspergillus species, and Mycobacterium intracellulare, as well as selective inhibition of yeast topoisomerase I. Toward this goal it is proposed to: (1) synthesize a series of rationally designed structural analogs of topoisomerase I eupolauridine for antifungal SAR studies; (2) evaluation in vitro activities of compounds against the opportunistic pathogens Cryptococcus neoformans, Candida albicans, and Mycobacterium intracellulare; (3) evaluate the inhibition of yeast and mammalian topisomerase I; (4) assess the selectivity of activity of the most active compounds from Specific Aims 1 and 2 by eval-uating their toxicities to mammalian cell culture (Vero and H9) to resident peritoneal macrophages and by evaluating them for gerotoxicity; (5) select the most promising candidates(s) for further study and to evaluate the efficacy of such candidates in appropriate animal models of disseminated infection; and (6) select and prioritize the most efficacious compound(s) for further derivatization to improve administration and delivery to the site of infection (i.e., bioavailability and pharmacokinetics).